Traditional laminates for printed circuits usually employ brominated flame retardants to achieve flame retardancy, and especially employ tetrabromobisphenol-A epoxy resin. Such brominated flame retardant has good flame retardancy but generates hydrogen bromide gas when being combusted. In addition, dioxin, dibenzofuran and other cancerogenic substances have been detected in combustion products of halogen (such as bromide and chloride, etc.)-containing electrical and electronic equipment wastes for the past few years, therefore the application of brominated epoxy resins is under restrictions. Two European Union environment-protecting directives of “waste electrical and electronic equipment” and “the restriction of the use of certain hazardous substances in electrical and electronic equipment” have been officially implemented on Jul. 1, 2006, and the development of halogen-free flame retardant copper-clad laminates has become a hot spot in the industry. Each copper-clad laminates manufacturer has sequentially put forwards its own halogen-free flame retardant copper-clad laminates.
Along with high speed and multi-functionalization in information processing of electronic products, application frequency has been constantly increased. Except for maintaining higher requirements for thermal resistance of laminate materials, dielectric constant and dielectric dissipation value are requested to be increasingly low. Accordingly, reducing Dk/Df has been a hot spot pursued by baseboard practitioners.
Traditional FR-4 materials generally employ dicyandiamide as hardener. Such hardener has tertiary reactive amine and possesses good process operability. However, since its carbon-nitrogen bond is relatively weak, likely to crack at high temperature, so the thermal decomposition temperature of cured products is low, which is unable to meet the thermal resistance requirement of lead-free process. Under this background, along with the large-scale implementation of lead-free process in 2006, phenolic resins started to be used as hardener for epoxy in the industry. Since phenolic resins has a benzene ring structure of a high density, the thermal resistance of the system after curing with epoxy is excellent, but meanwhile the dielectric performances of the cured products have a tendency of degradation.